Short in electrical system related to power master brake

[ronbo65]

Hi, I have an 87 GN, all stock. The car is not a daily driver with about 25k. Here's my problem. I recently replaced the battery and while checking for shorts before hooking up the new battery, I noticed there was a short in the system (while using a tester light). I determined that the short is related to fuse #14- which is for the powermaster brakes. (When I took out the fuse the light on the tester light went off.) I pulled out the main plug on the power unit and the switch on unit and the light on tester light was still on. Does anyone have any solutions to this problem.

Thanks,

 

[TurboDave]

Ummm, shorts??? The only thing noid lights can indicate is that there is power to the point you're probing. How are you thinking that's a short???

"(When I took out the fuse the light on the tester light went off.) "
Well yes of course. when you removed the fuse you removed the source of power, hence the light went out.

 

[ronbo65]

My father is a mechanic, and while checking the car for shorts after replacing the battery, he determined that the short is related to that fuse, i.e. the brakes, which are electronically controlled. The tester light was set on the battery. If there were no shorts in the system, the light would not have lit up. So since the light went off after the fuse was removed, the source of the problem might be related to the electronic braking system. Since the electronic brake system was unique to the grand national he is not sure how to correct.

 

[Ormand]

My car has a PowerMaster, and it is controlled by the brake pedal, which, in turn, is controlled by my foot. No electronics to it. Maybe your father was confused? The only "electronic control" in the PM is a pressure switch, which screws into the top of the master cylinder and turns the motor on/off. The power to the motor also goes to the coolant fan delay relay, so that may be stuck, causing a constant drain.

 

[ronbo65]

Thanks Ormand,
I will check that out, but I believe I am correct. If you look at the fuse box and manual you will see that this fuse is related to the brakes. Maybe it is different in the t-types, I am not sure. But when you take out that fuse, the brakes will not stop the car. The brake pedal becomes very hard and you cannot even push it down to the floor and stop the car. (When I put back the fuse, the brakes functions properly)

 

[Jbenn911]

That fuse you pulled is more than likely the power for the electric motor that runs the powermaster system..When I first bought my car, it had no brakes, turned out one of the wires that fired up the pump had a cut in it, and kept popping the fuse...Get a wiring diagram and check out the lines for the pump motor as well as the pressure switch, think the white one is the key one..

HTH

 

[Ormand]

I believe I am correct

Sorry to disappoint you- but you are not. There is no difference between the "T" types, as you suggest, and the GNs. When you come on this board and ask for advice, you might start by not assuming that you know more than we do. As jbenn911 points out, the fuse you pulled probably supplied power to the motor. Just keep on trying things, with no real idea of what you are doing, and you may make an expensive mistake.

 

[gbsean]

just wondering how you determined it was a short with a test light. If it is related to #14 that fuse should pop. I had problem with the pressure switch so the accumulator motor kept running and would pop the fuse.

 

[TurboDave]

That's what I was wondering. The ONLY thing that test light is going to show is that power is applied. Pull the fuse, and power is no longer supplied, hence no light. Replace the fuse and the powermaster has power available, this lights the light. Of course the brakes will work with the fuse and not without.
You can't use a noid light to find shorts. It's used to check for the presence or absence of voltage.

Short circuits will blow fuses. Do you have a problem blowing fuses?????????????

 

[ronbo65]

Ormand,
First of all, I am not coming on this website thinking that I know everything. I came on this site to find a solution to a problem that I have with my car. I read your response and I felt that you did not fully understand what I was saying. So I then further clarified what the problem was and how I arrived at my conclusion.

I also did not appreciate your comment --"My car has a PowerMaster, and it is controlled by the brake pedal, which, in turn, is controlled by my foot. No electronics to it." When you respond to people you should not have an attitude. Is that the proper way to answer a question from someone who has a problem??? You should watch what you say. If you think you know everything it DOES NOT give you the right to make these stupid comments. I truthfully don't need to hear that type of commenton this website. I am coming here for help not for attitude.

 

[ronbo65]

Hey turbo dave,
No, I don't have problems blowing fuses. And the noid light was only the first step to determine if I might have a short when putting in a new battery. Maybe I am not explaining this properly, but after I replaced the battery, I then checked to see if there might be any shorts that might be draining the battery. I saw that there was one (because the noid light was lit). I then proceeded to check all the fuses in the fuse box first to see where the short my possibly be coming from. That is how I arrived at that fuse. I am not sure where to proceed from here. That is why I am coming to this site for help.
Thank you for any help you might possibly have.

 

[ronbo65]

Hey JBenn911,
Yes, this fuse is the power for the electric motor on the powermaster system. I will look at a wiring diagram and see if the wires are ok.

Thanks

 

[gbsean]

you really need an ohm meter to determine where your current draw is coming from. If you have an alarm system that will draw current also radio clock and memory in some of the older cd players etc. Do you have an amp in the trunk. the fan relay has power to it at all times which is also hooked up to the power master brake switch. Ever notice how if the car is hot and you turn it off and the fan may run for a minute or two without the keys in. Maybe this is part of your false "short". Does the battery lose it's juice overnight or over a period of days or weeks.

 

[salvageV6]

Y'all need to take a few steps back and breathe a bit.

A test lamp in series with the hot lead or ground lead for that matter, (bulb type), will show current draw by lighting up with current flow.

Pulling the brake fuse can make it go out especially if the damm useless delay relay is still on the car and fubar.

Or key on and the power master pump was trying to run.

Clarifying what tests were actually run is important, then you can jump on the guy.

And no the description of the tests isn't very clear that's for sure but it sounds like perhaps someone else helped with the testing and determination, now how did I assume that? Guessed.

Lastly an ammeter would be the best tool to use in series with a battery cable whilst checking the fuses for draw.